Perl Scripting on Linux

Script 1: Adding the numbers 1 to 100, Version 1

$top_number = 100;
$x = 1;
$total = 0;
while ( $x <= $top_number ) {
 $total = $total + $x; # short form: $total += $x;
 $x += 1;  # do you follow this short form?
}

print "The total from 1 to $top_number is $total\n";
                  

Script 2: Adding the numbers 1 to 100. Version 2

This script uses a form of the for loop to go through the integers 1 through 100:

$total = 0;

#the for loop gives $x the value of all the 
#numbers from 1 to 100; 
for $x ( 1 .. 100 ) { 
 $total += $x;    # again, the short form            
}

print "The total from 1 to 100 is $total\n"; 
                  

Script 3: Printing a menu

This script uses an array to store flavors. It also uses a terrific form of the for loop to go through them. 

@flavors = ( "vanilla", "chocolate", "strawberry" );

for $flavor ( @flavors )  {
 print "We have $flavor milkshakes\n";
}

print "They are 2.95 each\n";
print "Please email your order for home delivery\n";

Script 4: Going one way or the other:

This allows you to program in a word to make a decision. The "ne" in the if statement stands for "not equal" and is used to compare text. The "die" statement shows you a way to get out of a program when you're in trouble.

#You can program answer to be heads or tails
$answer = "heads";

if ( $answer ne "heads" and $answer ne "tails" ) {
 die "Answer has a bad value: $answer!";
}

print "Answer is programmed to be $answer.\n";

if ( $answer eq "heads" ) {
 print "HEADS! you WON!\n";
} else {
 print "TAILS?! you lost. Try your coding again!\n";
}
                  

Script 5: Going one way or the other, interactively:

This allows you to type in a word to make a decision. A shameless sneak peek at the next lesson on input and output. <STDIN> allows us to read a word from the keyboard, and "chomp" is a function to remove the newline that's attached to our answer after hitting the carriage return.

print "Please type in either heads or tails: ";

#The <STDIN> is the way to read keyboard input
$answer = <STDIN>;
chomp $answer;

while ( $answer ne "heads" and $answer ne "tails" ) {
 print "I asked you to type heads or tails. Please do so: ";
 $answer = <STDIN>;
 chomp $answer;
}

print "Thanks. You chose $answer.\n";
print "Hit enter key to continue: ";

#This line is here to pause the script
#until you hit the carriage return
#but the input is never used for anything.
$_ = <STDIN>;

if ( $answer eq "heads" ) {
 print "HEADS! you WON!\n";
} else {
 print "TAILS?! you lost. Try again!\n";
}